Wire bonding apparatus

ABSTRACT

An apparatus for bonding wires on semiconductors is provided with a processor controlled vertical drive mechanism coupled to a novel bonding head of the type having a bonding tool mounted therein. The height of the bonding tool at the reset position and at the bonding position may be programmed into the processor for different semiconductor devices or workpieces. Indicating means are provided on the novel bonding head for establishing the reset position and the bonding positions so that the bonding tool is taught a series of predetermined vertical positions during a bonding cycle. The apparatus is also programmed to compute intermediate positions between said predetermined vertical positions to obtain optimum high speed movement of the bonding head and the bonding tool during subsequent bonding cycles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a processor controlled linear driveapparatus employed in automatic bonders and more particularly to aprocessor controlled Z drive motor for automatically positioning a wirebonding tool relative to the bonding pads of a semiconductor to be wirebonded at the first and second bond positions.

2. Description of the Prior Art

Automatic wire bonders have been made which have incorporated processorcontrolled X-Y tables coacting with the vertically moving bonding head.A bonding machine of this prior art type was made and sold by Kulicke &Soffa Industries, Inc. of Horsham, Pennsylvania as a Model 1412Automatic Ball Bonder. The vertical movement of the bonding head of thisprior art wire bonder was positioned by cams driven by a motor. Themotor employed a dynamic braking apparatus and prior art positioningmeans for positioning the bonding tool.

Heretofore, numerical controlled machine tools were available whichemployed cutting heads capable of being positioned in more than threeaxes. The data stored in the memory of the processors of such prior artmachine tools was provided by programmers working from drawings andencoding drafting tables of the type made and sold by Gerber ScientificCompany of Connecticut.

Numerical controlled machine tools are known to have processorcontrolled cutting heads movable under controlled programs which wouldcontrol the position of the cutting head in the Z axis or verticaldirection. Such prior art program controlled machine tools have beendriven through a first cutting operation to obtain data and to store thedata in the memory of the processor so that identical subsequent cuttingoperations could be repeated. The usual means for driving the cuttingheads of such prior art automatic machine tools are drive motors actingthrough relatively slow lead screws and are not suitable for positioningbonding heads of bonding machines.

Heretofore, fast acting lead screw drives have been employed in X-Ytables used on semiconductor bonding machines. Such X-Y tables have beenmade and sold by Kulicke & Soffa Industries Inc. in the aforementionedModel 1412 Automatic Ball Bonder. The high speed lead screw drives insuch X-Y tables have been found to be too slow to obtain optimum speedsfor driving a bonding head of a wire bonding machine.

It would be extremely desirable to provide a relatively inexpensive,reliable and extremely fast acting Z motor drive for positioning thebonding head of an automatic wire bonder.

SUMMARY OF THE INVENTION

It is a primary object of the present invention to provide a high torquemotor drive apparatus for positioning a wire bonding head at the highestpossible speed without creating excessive undamped vibrations and jerk.

It is another object of the present invention to provide a high torquemotor driven bonding head which settles or damps the induced vibrationsin a short period of time so as to enhance or optimize the bonding time.

It is another object of the present invention to provide a processorcontrolled motor drive for positioning a bonding tool as fast aspossible near a bonding position and to approach the bonding position atconstant velocity to control the impact forces acting through thebonding tool on the workpiece to be bonded.

It is another object of the present invention to provide a processorcontrolled motor drive for minimizing the constant velocity approach ofa bonding tool to a bonding position so as to optimize the bonding cycletime.

It is another object of the present invention to provide a processorcontrolled motor drive which is capable of teaching itself the verticalposition of the bonding tool where a constant velocity approach of thebonding tool toward the bonding position is to begin.

It is another primary object of the present invention to provide a novelbonding head for an automatic high speed wire bonder which is driven bya processor controlled drive motor to enable the bonding tool to engagethe bonding target with a minimum impact force before a major secondbonding force is applied which is capable of deforming and welding thewire to the workpiece to provide a strong wire bond.

In accordance with these and other objects of the present invention tobe explained in detail hereinafter there is provided a digital dataprocessor controlled Z drive apparatus for a semiconductor wire bondingmachine. A Z drive motor is mounted on a support frame and coupled to abonding tool holder means mounted on the support frame for moving thebonding tool in a vertical direction approaching a workpiece to bebonded. The processor controlled means comprises a program which isstored in the memory means for directing the bonding tool to a firstplurality of established predetermined vertical positions during abonding operation. The program means further comprises means forcomputing a plurality of variable predetermined vertical positions whichare intermediate the aforementioned established predetermined verticalpositions and stores these variable predetermined vertical positions inmemory. The program means further comprise means for sequentionallydirecting the bonding tool from one to the other of said sequentionallyestablished predetermined vertical positions by continuously directingthe Z drive motor to move said bonding tool to individual ones of saidplurality of variable predetermined vertical positions until the bondingtool reaches and touches the workpiece to be bonded. Thereafter abonding force is applied to the bonding tool by bonding force meanscooperating with the Z drive motor to apply predetermined force to thebonding tool.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation showing the preferred embodiment bondinghead and Z drive motor mounted on a frame of a wire bonding machine;

FIG. 2 is a side elevation of the bonding machine of FIG. 1;

FIG. 3 is an enlarged front elevation of the bonding head and Z drivemotor of FIGS. 1 and 2;

FIG. 4 is an enlarged side elevation of the novel bonding head and Zdrive means shown in FIGS. 1 and 2;

FIG. 5 is an enlarged plan view of the Z drive motor and bonding headshown in FIGS. 3 and 4;

FIG. 6 is an enlarged exploded isometric view of the novel bonding headshown in FIGS. 1 to 5;

FIG. 7 is a greatly enlarged isometric view of the novel sensor meansmounted on the novel bonding head shown in FIGS. 3 to 6;

FIG. 8 is a schematic drawing showing a sequence of operations of abonding tool and the associated wire clamping mechanism and wirefriction mechanism employed to shape a wire loop and to make apredetermined length of wire tail which assures a constant ball size;

FIG. 9 is a schematic diagram showing the height displacement of thebonding tool versus time during a bonding cycle; and

FIG. 10 is a schematic diagram of a typical microprocessor connected tothe feedback loops of a preferred embodiment Z drive motor showing how aprocessor can be employed to carry out the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Refer now to FIGS. 1 and 2 showing the front and side views of anautomatic ball bonder 10. Ball bonder 10 comprises a plurality ofcastings connected together to form a support frame 11 which is adaptedto support the illuminating lamp 12, the microscope 13 and the X-Y table14 which forms the support for workholder 15. Workholder 15 is adaptedto hold the workpiece in the form of a semiconductor and lead frame or ahybrid circuit on a substrate which will be wire bonded by bonder 10.The bonding wire 16 is supplied from reel 17 and is guided through afriction holding means 18 and wire clamp 19 into the bonding tool 21.The bonding tool 21 is moved in a substantial vertical axis by bondingtool holder 22 forming a part of bonding head 23. Bonding head 23further comprises a bonding tool lifter arm 24 which is coupled bycoupling means 25 to the Z drive motor 26. Z drive motor 26 comprises adrive shaft 27 onto which is mounted an eccentric crank 28. As will beexplained in detail hereinafter the drive motor 26 is adapted to movebonding tool 21 vertically down to a bond position and to execute afirst bond on the workpiece (not shown) mounted on the workholder 15.The bonding tool 21 is then raised paying out a loop of wire and the X-Ytable is moved so that the bonding tool 21 is opposite a new target onthe workpiece. The bonding tool 21 is then moved downward to the secondbond position where it executes a second bond and then is moved upward asmall distance where it stops. Clamp 19 is closed then permitting thebonding head comprising bonding tool holder 22 and tool lifter arm 24 tokeep moving in unison and to break the wire 16 at the second bondleaving a predetermined length of tail extending from the end of bondingtool 21. The wire tail (not shown) is raised further with the bondingtool 21 and clamp 19 clamped shut to a reset position so that theflame-off means 29 may ballize the wire tail prior to starting a secondbonding cycle.

Refer now to FIGS. 3 to 5 showing the bonding head 23 and Z drive motor26 in enlarged detail and to FIGS. 6 and 7 showing enlarged isometricviews of the bonding head and the novel sensing means. Bonding tool 21is shown in FIGS. 3 and 4 in the downward extended bonding positionwhere it has been driven by eccentric crank 28 mounted on shaft 27 ofmotor 26. The eccentric crank is adapted to move from the horizontalposition to approximately 80° below the horizontal and is adapted to beraised approximately 75° above the horizontal. It will be understoodthat these are the design limits of travel and that for ordinary bondingoperation the eccentric crank preferably moves approximately 45° fromeither side of horizontal. Movement of Z drive motor 26 is imparted tocoupling means 25 through bearing ball 31 held by a toe clamp 32 inbearing socket 33 of eccentric crank 28. Lower ball stud 34 is mountedin the housing of coupling means 25 and is provided with a bearing ball35 held by toe clamp 36 in a bearing socket 37 mounted on bonding toollifter arm 24. Vertical movement of coupling means 25 will impart apivoting movement to bonding tool lifter arm 24 which is mounted onsupport frame 11 by flexible pivot spring 38. The rear portion 39 of thepivot spring 38 is attached to the support frame 11. The outer arms 41of bonding tool lifter arm 24 are attached to the front and outerpivoting portions 42 of pivot spring 38. Keeper plates 43 are adapted toclamp and hold arms 41 to the outer and front pivot portions 42 ofspring 38. In a similar manner bonding tool holder mounting block 44 isprovided with a central mounting portion 45 which attaches to the frontcentral portion 46 of flexible pivot spring 38 and is held in place bykeeper plate 47. Bonding tool holder mounting block 44 is adapted tohold and clamp the bonding tool holder 22 shown as a transducer. Thebonding tool 21 is shown mounted in the end of transducer bonding toolholder 22. Downward movement of coupling means 25 imparts a pivotingmotion to bonding tool lifter arm 24 and to bonding spring 48 mountedthereon. The cantilevered end of bonding spring 48 is provided with anantifriction rod 49 which engages another antifriction rod 51 mounted inthe end of bonding tool holder mounting block 44. Thus arcuate movementof Z motor drive 26 exerts a force on rod 51 in the end of bonding toolholder mounting block 44 thus pivots the bonding tool holder 22 andexerts a force on the working face of bonding tool 21. A bonding spring48 is preferably biased in a manner which attempts to force lifter arm24 upward and bonding tool holder mounting block 44 downward. The biasof spring 48 will apply a preload bonding force on the bonding tool atthe time of engagement of the bonding tool with the workpiece. After themotor 26 further drives the coupling means 25 downward an additionalfinal bonding force is applied through the bonding springs to theworking face of bonding tool 21. Preferably the cantilevered shapedbonding force spring 48 has a linear rate so that the amount ofoverstroke is directly related to the bonding force applied at the timeof the bonding. Bonding spring 48 acts as a positive bonding spring andthe negative bonding spring 52 acts as a fine adjustment to reduce theforce of bonding spring 48. Bonding spring 52 is mounted between hangerpin 53 and the end of a pivoted lever 54 which engages an eccentric cam55.

As best shown in FIGS. 6 and 7 electrical contact member 56 is mountedin insulating bushings 57 which fit in apertures of clevis supports 58extending downward from bonding tool lifter arm 24. The contact 56serves as a stop pin for engagement by electrode contact 59 mounted inthe end of bonding tool mounting block 44. Electrode 59 is held in placeby nut 61 and screw 62. Electrode contact 56 is held in place by snaprings (not shown) which fit in grooves 63 of stop pin electrode contact56. Damper solenoid or bonding force solenoid 64 is mounted on lifterarm 24 and provided with a plunger 65 which engages electrode 59 causingit to be forced into contact with lower contact stop pin 56. When thebonding head is being driven at very high rates of acceleration in thedownward direction the inertia of bonding tool holder mounting blockurges it in a clockwise direction attempting to separate electrode 59from contact 56. During periods of rapid acceleration damper solenoid 64is energized to maintain contact 59 engaged with contact 56. Before thebonding tool reaches the pad or target electrode to be bonded thebonding tool passes through a short period of constant velocity movementand the damper solenoid 64 may be disengaged so that initial contact ofthe bonding tool 21 with the workpiece will cause the electrode 59 to beseparated from the contact electrode 56. This point is referred to asthe touchdown point or workpiece engagement point. It will be understoodthat the plunger of solenoid 64 can be energized to exert apredetermined downward force on contact 59 in a manner similar to thebonding force spring 48 acting on antifriction rod 51. Thus the bondingforce to be applied by bonding spring 48 may be applied by partiallyenergizing the damper solenoid 64 with a predetermined current.

Wire clamp 19 comprises a bracket 66 which is mounted on the end ofbonding tool lifter arm 24 by screws 67. A spring mounted actuating arm68 is also held by screws 67 and is provided with an antifriction disk69 at its outer movable end. Disk 69 engages the back of movable clampplate 71. Movable clamp plate 71 is spring biased in the open positionand is engageable with the front portion 73 of bonding tool lifter arm24 which serves as a fixed clamp plate. It will be understood thatdisk-shaped sapphire jewels are provided on clamp plates 71 and 73 toengage the wire which is fed through the guide 74. Actuating arm 68 isbiased by compression spring 75 to close clamp plate 71 against clampplate 73. Actuation of wire clamp solenoid 76 compresses compressionspring 75 and permits actuation arm 68 to be opened by spring bias andmovable clamp plate 71. In a similar manner friction holding means 18 isspring biased closed by spring arm 77.

Z drive motor 26 is provided with an encoder 78 which indicates therotary position of shaft 27 which is indicative of a position of thecrank arm 28 and in turn is indicative of the actual vertical positionof bonding tool 21. When bonding tool 21 is raised to its highest orreset position after completing a second or last bond there is a wiretail extending from the end of the bonding tool 21. Flame-off means 29is provided with a flame-off electrode 79 which is spring biased in theretracted position by a spring 81 as shown in FIG. 3. Flame-off solenoid82 is actuatable when the bonding tool 21 is in the retracted positionto move the flame-off electrode 79 under the end of the wire tail inclose proximity thereto. In the close proximity position the flame-offelectrode 79 is connected to a source of high voltage current. The highvoltage energy breaches the gap between the flame-off electrode 79 andthe end of the wire tail extending from the bonding tool 21 so as tomelt and ballize the end of the wire tail.

Flame-off elecrode 79 serves an additional purpose in that it is capableof establishing the reset position as well as establishing the height ofthe bonding tool 21 relative to the tip of the flame-off electrode 79which enables the bonding tool to be raised to the reset position sothat the wire tail is at the correct height relative to the flame-offelectrode when the ballizing current is applied. As best shown in FIG. 3flame-off electrode 79 can be moved into the path of bonding tool 21after it has been inserted into bonding tool holder 22. The bonding toolis then moved to the downward position until it engages the flame-offelectrode 79. As explained hereinbefore the engagement of the bondingtool 21 with sufficient resistance force causes the electrode contact 59to disengage electrical contact member 56 and the vertical position atwhich these contacts are open may be recorded in the memory of theassociated processor as will be explained in detail hereinafter. Thusthe bonding tool 21 may be raised a predetermined distance from itsengagement point with flame-off electrode 79 to be moved to a properreset position where ballizing of the wire tail would take place.

Anytime the contacts 56 and 59 are open the rotary position of encoder78 may be recorded in the memory of the processor. The rotary positionof encoder 78 is converted into the Z or vertical position of bondingtool 21 by a look-up table stored in the memory of the processor. Themanner in which the processor controls the Z drive motor will beexplained in detail hereinafter with the reference to FIG. 10.

Refer now to FIG. 8 showing in schematic form the movement of thebonding tool 21 relative to a workpiece 82 which is to be wire bonded.FIG. 8 shows the relative movement of the wire clamp 19 and frictionholding means 18 which controls the movement of the wire to form theloop. The alphabetic subnumbers on FIG. 8 are intended to indicatepositions of the bonding tool during a bonding cycle which will beexplained in greater detail with reference to FIG. 9. At position a ofFIG. 8 the bonding tool 22 is at its highest or reset position. Bondingtool 21 is vertically positioned by the processor control means at apredetermined distance above the flame-off means 29. This reset positionwas located by engaging the bonding tool 21 with the flame-off electrode79 to open the contacts 56, 59.

The friction holding means 18 which are fixed relative to the frame 11,comprise a pair of juxtaposed synthetic jewels 83, one of which ismounted on spring arm 77 and the other jewel is actuated by a solenoid(not shown). At position a the jewels 83 of friction holding means 18are closed and the wire clamp 19 is also closed. A small wire tail 83extends from the bonding tool 21 and has a ball 85 at the end thereof.The damper solenoid 64 is energized to clamp the contacts 56 and 59together to keep them from opening during rapid acceleration. Bondingtool 21 descends rapidly from the reset position toward the workpiece 82and the drag on wire 16 exerted by the holding means 18 causes thebonding tool 21 to move down the wire relative to the ball until theworking face of the bonding tool 21 engages the ball 85 as shown inposition b-. Bonding tool 21 moves both the wire 16 and the ball 85further down toward the first bond position on workpiece 82 until thefirst bond position is reached as shown in position d. When the ball 85engages the workpiece 82, damper solenoid 64 has been de-energized whichpermits the contacts 56, 59 to open indicating a Z touchdown position.Vertical downward movement of bonding tool 21 after the Z touchdownposition is reached is controlled by the amount of bonding force beingapplied to the bonding tool and this force is determined by theparticular type and size of wire and the type of bonding. When anultrasonic transducer bonding tool holder 22 is employed, the transducer22 is energized during the bonding operation starting at position d.Some types of bonds such as thermocompression bonds do not requireultrasonic scrub and ultrasonic transducers.

Friction holding means are opened at first bond position d as shown. Asbonding tool 21 is rapidly accelerated upward from the first bondposition to form a wire loop, the X-Y table 14 is moved to a positionwhich locates the second bonding target of workpiece 82 under thebonding tool 21 as shown in position f. Bonding tool 21 rises to the topof the predetermined loop height and friction holding means 18 are stillopen, but as the bonding tool 21 descends rapidly toward a second bondposition the friction holding means 18 are closed. It will be understoodthat both the loop heighth and the timing of the closing of the frictionholding means 18 are adjustable to permit shaping of the wire loop.Position g- shows the friction holding means 18 closed and the wireclamp 18 still open as the bonding tool 21 descends toward the secondbond position. Before reaching the second bond position wire clamp 19 isalso closed as shown in position g. During the period of rapidacceleration to the loop height and rapid deceleration to the secondbond position as shown in position i the damper solenoid 64 has beenenergized to hold contacts 56, 59 together and before reaching the bondposition damper solenoid 64 is de-energized which permits contacts 56,59 to open and to indicate the Z touchdown position at the second bond.Upon completion of the second bond wire loop 86 has been formed,friction holding means 18 and wire clamp 19 are open. Since the verticalposition of the second bond is known through opening of contacts 56, 59the bonding tool 21 may be raised a predetermined vertical distanceabove the Z touchdown position at the second bond to provide a length ofwire which will become the wire tail 84. After the bonding tool 21 israised relative to the wire, the clamp 19 is closed and continuingvertical movement of the bonding tool 21 and wire clamp 19 will breakthe wire tail 84 at the second bond leaving the wire tail extending fromthe bonding tool 21 as shown in position m-. The bonding tool 21 and thewire clamp 19 continue to move vertically upward to the reset positionwhere the bonding tool 21 stops, the friction holding means 18 close andthe flame-off electrode 79 is energized to ballize the wire tail 84 toprovide a ball 85 at the end thereof as shown in position m. The bondingtool 21 remains in the reset position until the X-Y table 14 is againmoved to place a new bonding target opposite the bonding tool 21 asshown in position a where a second bonding cycle is ready to start.

Refer now to FIG. 9 showing in greater detail the movement of theworking face of the bonding tool 21. At the reset position a the bondingtool 21 is typically 0.33 inches above substrate 82. The bonding targeton the substrate 82 has been positioned below the working face of thebonding tool and it is desirable to move the bonding tool 21 as fast aspossible to the first bond position and to complete the first bond. Ifthe bonding tool is accelerated to its highest or optimum velocity andthis velocity is maintained the bonding tool 21 will impact on thebonding target of the substrate 82 with a very high impact force whichmay destroy the workpiece and would not result in a proper bond.Accordingly, Z drive motor is accelerated to its highest permissiblevelocity considering the restraints placed on jerk, acceleration andvelocity as well as the current limitation of the Z drive motor 26. Thevertical descending path between points a and b of FIG. 9 is shown as astraight line. However, as will be explained hereinafter this path isnot linear but consists of an initial very high acceleration followed bya period of substantially linear velocity and ending with a period ofrapid deceleration at point b. At point b the bonding tool enters aperiod of linear velocity between points b and c. This permits theelements of the bonding head 23 to settle relative to each other so thatthe solenoid 64 clamping the contacts 56, 59 together may be releasedprior to the beginning of the bonding operation. At point c the Z drivemotor acting through coupling means 25 on bonding tool lifter arm 24 isoverstroked to apply a predetermined bonding force through the bondingspring 48 to antifriction rod 51 on bonding tool holder 21 thus applyinga predetermined bonding force on the working face of bonding tool 21. Atpoint d of FIG. 9 the bonding tool starts the squashing of the ball 85by applying the accumulative bonding forces comprising the initialimpact force, the initial force of bonding spring 48, some force fromthe solenoid plunger 65 and a small force from the pivot spring 38. Itwill be understood that all of these forces can be limited to under 20grams and that the main bonding force is adapted to be applied by theoverstroke movement which applies an additional force through bondingspring 48 of the order of magnitude of 10 to 80 grams. As explainedhereinbefore, the main bonding force applied by bonding spring 48 may beapplied by solenoid 64. The distance the working face of the bondingtool moved below the datum or first bond Z touchdown position is theamount of squashout applied to the ball 85. At position e the first bondis complete and the bonding tool is rapidly accelerated to thepredetermined loop height at position f. It will be understood thatrapid acceleration takes place near point e and rapid deceleration takesplace as the bonding tool approaches point f. In similar manner, rapidacceleration takes place leaving point f and rapid deceleration takesplace as the bonding tool approaches point g where it starts a period ofcontrolled constant velocity. The bonding tool impacts the bondingtarget on the workpiece 82 at point h with a controlled andpredetermined impact force opening the aforementioned contacts 56,59 andthe second bond is initiated. The second bond is squashed-out when thebonding tool reaches the point i and the bonding tool remains on thewire until the second bond is complete at point j. At point j the wireclamp 19 has opened and the bonding tool 21 rises a predetermined amountto point k where the bonding tool is stopped and the wire clamp 19 isclosed leaving a predetermined length of wire tail 84 extending from thebonding tool. The clamping operation is complete at point 1 and thebonding tool 21 again rises rapidly to the reset position breaking thewire tail 84 at the second bond. At the reset position m the flame-offelectrode is actuated by flame-off solenoid 76 and a high voltagecurrent is applied across flame-off electrode 79 to wire tail 84 toballize the wire tail 84 and provide a wire ball 85.

As described hereinbefore the reset height point a and m is set apredetermined distance above the contact point of the bonding tool 21with the flame-off electrode 79. It will be understood that this exactvertical heighth distance will vary from bonding machine to bondingmachine and from bonding tool to bonding tool. It is quite difficult toreplace a bonding tool in a bonding tool holder without incurring somechange of the distance of the vertical height of the bonding tool abovethe bonding target on the workpiece 82. Similarly the first bond Ztouchdown position at point c can be determined before the first bond ismade by slowly positioning the bonding tool on the first bond target andopening the aforementioned contacts 56, 59. Once the first bond Ztouchdown position c is located the inflection point b can be calculatedbecause it is a predetermined distance above point c. The velocity ofthe bonding tool between points b and c is determined by empirical dataobtained during the testing of a bonding machine. The constant velocitybetween points b and c is selected to avoid harmful impact forces whenthe bonding tool engages the bonding target on the workpiece 82. Insimilar manner the second bond Z touchdown position at point h may bedetermined before the second bond is made during an automatic bondingcycle and the inflection point g is calculated in the same manner as theaforementioned inflection point b.

One of the novel features of the present invention is the manner inwhich the inflection point positions b and g may be determined duringautomatic bonding operation employing the contacts 56, 59. For example,a plurality of different thickness and different height semiconductordevices may be connected to a substrate or to a printed circuit board ina hybrid configuration. The height of the individual semiconductordevices to be wire bonded vary substantially and if predeterminedtouchdown positions and inflection point positions are recorded inmemory during a teaching mode or teaching operation the information isof no practical use in wire bonding a second device of the same typebecause the vertical distances are changed. When bonding operations arebeing performed on this type of hybrid device the inflection point b ispreset to a higher predetermined inflection point position shown forpurposes of illustration as being at point b'. During the first cycle ofan automatic bonding operation the inflection points b' and g' areprogrammed into the inflection point positions to be used on the firstdevice to be bonded. When the first wire is bonded the first and secondbond Z touchdown position c and h are determined. With this actualinformation stored in memory of the processor the optimum inflectionpoints b and g can be computed for the second and subsequent wire bondson the same device.

It will be understood that in the present state of the art as many asseventy wire bonds may be made on a single device, thus, optimizing theinflection point so that the minimum constant velocity time betweenpoints b and c and points g and h will result in optimum or shorterbonding cycles.

Another feature of the present invention permits the operator of abonding machine to set the inflection points b and g very high during alearning or teaching mode so that the bonding tool can be positionedaccurately and the optimum inflection points b and g located withoutdamaging the workpiece.

To provide a better understanding of the manner in which the novelbonding head can supply information to enable the processor to computeits own optimum vertical approach to bonding targets on the workpiecethe time for the bonding tool 21 to travel from one to another of thepositions shown in FIG. 9 has been placed on FIG. 9. Since theinflection points b and g, the touchdown points c and a, the loop heightf and the reset height a and m is variable from device to device, toobtain the optimum and shortest bonding cycle, it would be impossible tostore in the memory of a processor all of the data that would berequired to control the motion of the bonding tool in a manner similarto point to point control as employed in numerical control machinetools.

Accordingly, there is provided a novel method of positioning the bondingtool between the predetermined points a and b during a bonding operationand between the other predetermined points shown on the bonding cycletime curve in FIG. 9. Refer also to FIG. 10 showing in schematic form ablock diagram of a prior art processor connected to drive the Z drivemotor 26 in a manner which will position the bonding tool atpredetermined vertical heights as illustrated in FIG. 9. Z drive motor26 is a commercially available D.C. servo motor tachometer generator ofthe type similar to Models E-530-2 available from Electro-CraftCorporation of Hopkins, MN. for tape transport drives. The opticalencoder 78 is preferably RENCO KT 23 series having at least 800 lineresolution available from RENCO Corporation of Goleta, CA.

Generator 87 provides a voltage signal indicative of the rotationalvelocity of motor 26 on line 89 which is representative of a voltagefeedback loop of a typical servo motor. Encoder 78 provides an encodedsignal output on line 91 indicative of the actual rotary position of Zdrive motor 26. Encoder converter 92 converts the two bit Gray code online 91 to a digital data output on line 93 which is representative ofthe actual angular position of the Z drive motor and its connectedeccentric crank 28. The encoder converter 92 supplies data representingthe changing actual angular position of motor 26 to the arithmetic logicunit (ALU) 95 of processor 100 under control of the processor controlunit 103. Processor 100 is preferably a commercially availablemicroprocessor of the type similar to that sold by Motorola Inc. asModel M6800 or an equivalent type ITEL 8080 Series Microprocessor. Asschematically shown, the processor 100 is provided with a keyboard 101and a peripheral interface adapter (PIA) by which an operator canmanually initiate machine functions. The control unit follows sets ofinstructions, stored in memory 105, for each machine function. Theaddress latch 104 is adapted to address the various portions of memory105 which contain, in addition to the instructions to the control unit,results of calculations representing positions of the bonding toolintermediate predetermined points a and b, etc.; data look-up tables,the variable constraints which are placed on the curves empiricallyderived to define the jerk and maximum jerk, the acceleration andmaximum acceleration and the maximum velocity at which the Z drive motor26 is to be driven. It will be understood that constraints apply to theaforementioned drive curves. Such constraints are well known and aredescribed in text books and are available from manufacturers of servomotors. It is sufficient to say for purposes of this invention that theconstraints will limit the amount of maximum jerk and the time duringwhich the pulses of the jerk curve are applied. Further, the constraintswill limit the maximum acceleration of the Z drive motor and will alsolimit the time during which the empirically derived acceleration curvemay be applied to the Z drive motor 26. The constraints further providethe shortest machine motion times consistent with a smooth drive curveof the trapezoidal acceleration type empirically derived for the systemto which the Z drive motor is applied. Memory 105 may also comprise afloppy disk or similar auxiliary peripheral memory system for storingprograms beyond the scope of the limited memory of microprocessor 100.

In the preferred embodiment illustrated in FIGS. 9 and 10, the distancebetween points a and b is divided into milliseconds. The position of thebonding tool at point a is known. The predetermined position b is known.The position along the curve shown in FIG. 9 between points a and b ateach millisecond may be computed by the processor 100 because the limitsof jerk, acceleration and velocity and the type of travel (highvelocity) is known. All of the points intermediate predetermined pointsa and b may be calculated for every millisecond of travel and stored inthe memory 105. When bonding tool 21 is instructed to move from positiona to its first calculated position Z₁, the desired Z₁ vertical positionis supplied via path 96 as an address to address latch 104. The addresslatch 104, under control of the control unit 103, addresses the look-uptable in memory 105 via line 97 and converts the desired Z₁ position(address) to a desired rotary position Z₁ R in digital form on line 98to the ALU 95. Each millisecond the clock signal on line 99 enables theactual rotary position of motor 26 and the next desired rotary positionZ_(n) R of the motor 26 to be read via lines 93 and 98 to the ALU 95which subtracts the difference and converts the difference to adifference or error signal on line 106. It will be understood that ALU95 is not only a subtracer, but is used to perform other calculationsand manipulations for machine functions. The output signal on line 108is amplified at amplifier 109 and applied to Z drive motor 26 via line111.

Each millisecond the clock signal on line 99 generates new Z desiredpositions and desired motor rotary positions ZR so that the Z drivemotor is instructed to drive at the predetermined jerk, acceleration andvelocity to the next sequential Z_(n) desired position. Beyond point b,during the constant velocity descent, a series of Z_(n) points is usedin the manner described for a to b motion, to yield a constant velocityZ motion. In a similar manner the Z points or vertical heights may becomputed between the predetermined positions b and c, e and f, f and g,g and h, j and k, and finally l and m. It will be understood that theintermediate Z_(n) points or positions are not fixed but depend on thepredetermined bonding heights and reset heights determined on eachparticular device. Thus, it is preferred that all the points necessaryto position the bonding tool 21 between positions a and e,representative of a first bond operation, and j and g, representative ofa second bond operation, are calculated and stored in memory 105 shortlybefore the bonding tool 21 is driven through a bonding cycle. In thepreferred embodiment, the memory 105 of processor 100 is capable ofstoring more than two complete bonding cycles including thepredetermined positions and the variable Z_(n) positions ahead of theactual movement of the bonding tool. Processor 100 is capable ofcarrying out these operations faster enough so there is no delay incompleting consecutive automatic wire bonding operations.

Having explained a preferred embodiment of the present invention whichoptimizes the time required for a bonding cycle to a minimum byemploying self teaching during the actual automatic bonding cycles, itwill be understood that modifications to the teachings could be made tothe novel self teaching contacts 56, 59 or to the novel bonding head 23.Further, if the automatic wire bonder 10 is not required to operate asfast as it is capable of operating during its optimum bonding cycle,additional predetermined Z positions may be incorporated in memory todrive the bonding tool 21 between predetermined points at accelerationsand velocities that are less than optimum.

The principal advantage of the present wire bonder is that it does notrequire critical manual adjustment to be able to operate in the optimumautomatic mode. All of the critical predetermined vertical positions aretaught to the memory of the processor and are not mechanically set. TheX-Y positions are also taught in a learning mode sequence of operations.

It will be appreciated from examination of FIG. 9 that a completebonding cycle may be performed in one quarter of one second for eachwire bonded. This time is much faster than speeds achieved by prior artbonders.

We claim:
 1. A processor controlled vertical drive apparatus for abonding machine comprising:a support frame, a bonding head mounted onsaid support frame for vertical movement relative thereto, a Z drivemotor mounted on said support frame for positioning said bonding head,said bonding head comprising a bonding tool lifter arm coupled to said Zdrive motor, first sensor means on said bonding tool lifter arm, saidbonding head comprising a bonding tool holder operable by and alsooperable relative to said bonding tool lifter arm, second sensor meanson said bonding tool holder, a bonding tool mounted in said bonding toolholder for performing a bonding operation on a workpiece, and means fordetecting when said sensors are together or apart, thereby indicatingwhen said bonding tool has first engaged said workpiece.
 2. A processorcontrolled vertical drive apparatus as set forth in claim 1 whichfurther includes:position indicating means connected to said Z drivemotor for providing an output signal indicative of the vertical positionof said bonding tool, and processor control means coupled to said outputsignal and having a memory for storing data indicative of the verticalposition of said bonding tool.
 3. A processor controlled drive apparatusas set forth in claim 2 wherein said Z drive motor is a rotary motor andsaid position indicating means comprises an encoder for generating adigital data output signal indicative of the rotary position of said Zdrive motor.
 4. A processor controlled drive apparatus as set forth inclaims 3 which further includes:a crank arm on said Z drive motor, andlink means connecting said crank arm to said bonding head.
 5. Aprocessor controlled drive apparatus as set forth in claim 2 whichfurther includes:means for connecting said tool lifter arm to saidbonding tool holder so that they are moved in unison by said Z drivemotor.
 6. A processor controlled drive apparatus as set forth in claim 5wherein said means for connecting said tool lifter arm to said bondingtool holder comprises an electromechanical clamp.
 7. A processorcontrolled drive apparatus as set forth in claim 6 wherein said firstand said second sensor means comprise electrical contacts adapted toprovide signals indicating whether said contacts are opened or closed.8. A processor controlled drive apparatus as set forth in claim 7wherein said electromechanical clamp comprises a solenoid mounted onsaid bonding tool holder adapted to bias said contacts into a closedposition.
 9. A processor controlled drive apparatus as set forth inclaim 6 wherein said electromechanical clamp comprises a solenoidadapted to yieldably couple said bonding tool holder to said tool lifterarm.
 10. A processor controlled vertical drive apparatus as set forth inclaim 1 which further includes:processor control means for recording thevertical touchdown Z position of said bonding tool when it first engagessaid workpiece, program means in said processor control means forgenerating a tolerance inflection point representative of a verticalposition higher than said touchdown Z position, and said program meansfurther comprising means for driving said Z drive motor to displace saidbonding tool in a vertical direction at substantially constant velocitybetween said tolerance inflection point and said touchdown Z positionand at varying and at higher maximum velocities when approaching saidtolerance inflection point.
 11. A processor controlled vertical driveapparatus as set forth in claim 10 wherein said tolerance inflectionpoint generated by said program means is a predetermined verticaldistance above said touchdown Z position.
 12. A processor controlledvertical drive apparatus as set forth in claim 11 wherein said toleranceinflection point generated by said program means is manually alterablefor a first bonding cycle and is program selectable for subsequentbonding cycles.
 13. A processor controlled vertical drive apparatus asset forth in claim 11 wherein said tolerance inflection point generatedby said program means is program selectable for both a first bondingcycle and subsequent bonding cycles, and is alterable between said firstand said subsequent bonding cycles depending on the location of said Ztouchdown position detected on said first bonding cycles whereby thetolerance inflection point may be optimized for bonding cycles on thesame workpiece.
 14. A processor controlled vertical drive apparatus asset forth in claim 1 which further includes:processor control means fordetermining the vertical touchdown Z position of said bonding tool whenit just engages said workpiece, and means for yieldably connecting saidtool lifter arm to said bonding tool holder, said means for yieldablyconnecting said tool lifter arm to said bonding tool holder beingactivated before vertical touchdown Z position is reached and yieldablydeactivated during a bonding operation.
 15. A processor controlledvertical drive apparatus as set forth in claim 14 which furtherincludes:bonding force spring means yieldably coupling said tool lifterarm to said bonding tool holder, said processor control means beingadapted to move said Z drive motor to position said bonding tool lifterarm to a predetermined position lower than said touchdown Z positionwhereby a bonding force is applied to said bonding tool by said bondingtool lifter arm acting through said bonding force spring means.
 16. Aprocessor controlled vertical drive apparatus as set forth in claim 15which further includes:a negative bonding force spring coupled betweensaid bonding tool lifter arm and said bonding tool holder, and adjustingmeans for adjusting the amount of negative bonding force applied by saidnegative bonding force spring.
 17. A processor controlled vertical driveapparatus as set forth in claim 14 wherein said means for yieldablyconnecting said tool lifter arm to said bonding tool holder comprises adamper bonding force solenoid;said solenoid being energizable atdifferent current levels to exert different coupling forces between saidtool lifter arm and said bonding tool holder, said processor controlmeans being adapted to move said Z drive motor to position said bondingtool lifter arm to a desired predetermined vertical position to causesaid damper bonding force solenoid to apply a predetermined bondingforce to said bonding tool.
 18. A processor controlled vertical driveapparatus as set forth in claim 10 which further includes:flame-offmeans movably mounted on said support frame to enable said bonding toolto be engaged therewith, said processor control means being adapted torecord the vertical height of said bonding tool when said bonding toolengages said flame-off means, said program means further comprisingmeans for computing a bonding tool reset position a predetermineddistance above said position where said bonding tool engaged saidflame-off means.
 19. A processor controlled vertical drive apparatus asset forth in claim 18 which further includes:a bonding wire in saidbonding tool, means for clamping said wire when said bonding tool hasmoved from said bond position to a plateau position to cause said wireto be fed through said bonding tool a predetermined distance to providea predetermined tail length.
 20. A processor controlled vertical driveapparatus as set forth in claim 19 wherein said flame-off means arepositioned by said processor control means to the near proximity of theend of said predetermined length of wire tail and are adapted to ballizesaid wire tail to provide a predetermined ball size when said bondingtool is in a reset position.
 21. A processor controlled vertical driveapparatus as set forth in claim 20 wherein said flame-off meanscomprises a flame-off electrode adapted to be moved into the closeproximity of the end of said wire tail by a flame-off solenoid, andmeansfor initiating a high voltage discharge between the end of said wiretail and said flame-off electrode.
 22. A processor controlled verticaldrive apparatus as set forth in claim 20 which further includes:frictionmeans for applying a friction drag to said wire when said bonding toolis moved from said reset position toward a first bond position to enablesaid bonding tool to be moved relative to said ball until said ballengages the working face of said bonding tool.
 23. A processorcontrolled linear drive mechanism for converting rotary motion topredetermined linear motion comprising:a support frame, a drive motormounted on said support frame, rotary position indicating meansconnected to said drive motor, eccentric drive means connected to saiddrive motor, a driven follower member connected to said eccentric drivemeans, said driven follower member being guided for movement in a linearmotion path, processor control means having a memory for storing digitaldata indicative of different increments of rotational movement of saiddrive motor, said different increments of rotational movement beingindicative of predetermined linear movements of said driven followermember, said rotary position indicating means providing an outputposition signal coupled to said processor, and arithmetic means in saidprocessor for comparing said output position signal with one of saiddigital data indications of a predetermined increment of rotationalmovement of said drive motor and for producing a forcing function signalcoupled to said drive motor indicative of the difference between adesired predetermined linear position and the actual linear position ofsaid driven follower member, whereby said drive motor forcing functionsignal is varied to position said drive motor at variable rates ofchange.
 24. A processor controlled linear drive mechanism as set forthin claim 23 wherein said rotary position indicating means fordetermining the dynamic position of said drive motor comprises anencoder connected to said drive motor.
 25. A processor controlled lineardrive mechanism as set forth in claim 1 wherein said eccentric drivemeans comprises a crank arm and a link pivotally connected thereto,andwherein said driven follow member comprises a tool lifter armconnected to said link, a bonding tool holder movably mounted on supportframe, and yieldable coupling means for connecting said tool lifter armto said bonding tool holder for moving said tool lifter arm and bondingtool holder in unison.
 26. A processor controlled linear drive mechanismas set forth in claim 23 wherein said processor control means comprisesa look-up table in said memory for converting desired linear positionsof said driven follower member to predetermined desired rotationalpositions of said drive motor.
 27. A digital data processor controlledlinear drive apparatus for converting rotary motion to a predeterminedlinear motion, the combination comprising:a support frame; a drive motormounted on said support frame, rotary position indicating meansconnected to said drive motor, eccentric drive means connected to saiddrive motor, a driven follower member connected to said eccentric drivemeans, said driven follower being guided for movement in a linear motionpath, processor control means of the type having a memory for storingdigital data and means for performing arithmetic computation on saiddigital data, program means stored in said memory means for generating adigital address indicative of a desired linear position of said drivenfollower member, conversion means stored in said memory means forconverting a desired digital address position to digital data indicativeof a desired rotary position of said drive motor, said arithmetic meansof said processor control means being adapted to substract thedifference between said desired rotary position of said drive motor andthe digital position of said drive motor indicated by said rotaryposition indicating means, and means for converting the arithmeticdifference between said drive motor position and said desired positioninto an analog current signal coupled to said drive motor for drivingsaid driven follower to said linear desired position.
 28. A processorcontrolled drive apparatus for a semiconductor wire bonder comprising:asupport frame, a Z drive motor mounted on said support frame, bondingtool holder means mounted on said support frame for movement in avertical direction by said Z drive motor, a bonding tool mounted on saidbonding tool holder means, sensing means on said bonding tool holdermeans actuated by said bonding tool when said bonding tool engages atouchdown Z position during a bonding operation, processor control meansfor recording said touchdown Z position of said bonding tool when itengages said workpiece, program means in said processor control meansfor generating an inflection point representative of a Z position higherthan said touchdown Z position, and said program means furthercomprising means for driving said Z drive motor to displace said bondingtool in a Z direction at substantially constant velocity between saidinflection point and said touchdown Z position and at varying velocitieswhen approaching said inflection point.
 29. A processor controlled driveapparatus as set forth in claim 28 wherein said bonding tool holdermeans comprises:a lifter arm coupled to said Z drive motor, a bondingtool holder mounting block, and a bonding tool holder mounted in saidbonding tool holder mounting block for supporting said bonding tool, andwherein said sensing means comprises a first sensor element on saidlifter arm and a second sensor element on said bonding tool holdermounting block.
 30. A processor controlled drive apparatus as set forthin claim 29 which further includes:means for yieldably coupling saidtool lifter arm to said bonding tool holder mounting block.
 31. Aprocessor controlled drive apparatus as set forth in claim 30 whereinsaid means for yieldably coupling said tool lifter arm to said bondingtool holder mounting block comprises a solenoid having a movablesolenoid plunger mounted on said lifter arm,a pin on said mounting blockengagable by said solenoid plunger for urging said pin to engage a stopon said lifter arm for clamping said pin to said stop when said solenoidis actuated.
 32. A processor controlled drive apparatus as set forth inclaim 31 wherein said pin and said stop provide electrical contacts forsaid sensor elements of said sensing means adapted to be opened whensaid solenoid is not actuated and when said bonding tool engages saidtouchdown Z position.
 33. A processor controlled drive apparatus as setforth in claim 32 wherein said solenoid is actuated to clamp said pin tosaid stop to mechanically couple said bonding tool holder mounting blockto said lifter arm during periods of rapid acceleration.
 34. A processorcontrolled drive apparatus as set forth in claim 33 wherein saidsolenoid is not actuated during a bonding operation to uncouple saidbonding tool holder mounting block from said Z drive motor.
 35. Aprocessor controlled drive apparatus as set forth in claim 32 whereinsaid solenoid is partially actuated with a predetermined current topartially couple said bonding tool holder mounting block to said lifterarm during a bonding operation for transmitting a predetermined bondingforce to said bonding tool.
 36. A processor controlled drive apparatusas set forth in claim 30 which further includes a bonding force springcoupled between said bonding tool holder mounting block and said lifterarm adapted to bias them in the same direction as said yieldablecoupling means.
 37. A processor controlled drive apparatus as set forthin claim 36 wherein said yieldable coupling means comprises a solenoidhaving a solenoid plunger spring biased in a direction to normally applya coupling force which adds to the force of said bonding force spring.38. A processor controlled drive apparatus as set forth in claim 37which further includes a negative bonding force spring coupled betweensaid bonding force lifter arm and said bonding tool holder mountingblock.
 39. A processor controlled drive apparatus as set forth in claim28 which further includes:flame-off means movably mounted on saidsupport frame to enable said bonding tool to be engaged therewith duringa teaching mode, and wherein said processor control means is adapted torecord the vertical height of said bonding tool at the time ofengagement with said flame-off means, and wherein said program means isfurther provided with means for moving said bonding tool to a resetposition having a predetermined height above said flame-off means.
 40. Aprocessor controlled drive apparatus as set forth in claim 39 whichfurther includes:a bonding wire in said bonding tool after completion ofa second bond, clamp means on said lifter arm adapted to clamp said wireafter said bonding tool and said clamp means are raised together apredetermined height to provide a wire tail extending from said bondingtool.
 41. A processor controlled drive apparatus as set forth in claim40 wherein said flame-off means comprises a flame-off electrode movableto the close proximity of the end of said wire tail when said bondingtool is raised to said reset position, andhigh voltage pulse means forapplying a voltage between said wire tail and said flame-off electrodeto ballize said wire tail.
 42. A processor controlled drive apparatusfor a semiconductor wire bonder as set forth in claim 29 which furtherincludes:bonding force means coupled between said bonding tool holderand said lifter arm for applying a bonding force therebetween, saidprogram means comprising means for driving said Z drive motor to engagesaid bonding tool with a workpiece to bond a wire at a first bondposition, said program means further comprising means for raising saidbonding tool to play out a loop of wire from said first bond positions,said program means further comprising means for lowering said bondingtool toward a second bond position, and friction means for applying afriction drag to said wire before said bonding tool reaches said secondbond position to provide a controlled loop height and shape between saidfirst and said second bond.
 43. A processor controlled Z direction driveapparatus for a semiconductor wire bonder comprising:a support frame, aZ drive motor mounted on said support frame, bonding tool holder meansmounted on said support frame for movement in the Z direction by said Zdrive motor, a bonding tool mounted on said bonding tool holder,processor control means comprising program means stored in memory meansfor directing said bonding tool to a first plurality of establishedpredetermined vertical positions during a bonding operation, saidprogram means comprising means for computing a plurality of variablepredetermined vertical positions intermediate two sequential positionsof said established predetermined vertical positions and means fortemporarily storing said variable predetermined vertical positions insaid memory means, and said program means comprising means forsequentially directing said bonding tool from one to the other of saidtwo sequential established predetermined vertical positions bycontinuously directing said Z drive motor to move said bonding tool toindividual ones of said plurality of variable predetermined verticalpositions.
 44. A processor controlled Z drive apparatus as set forth inclaim 43 wherein said bonding tool is adapted to be moved between twosequential positions in a predetermined length of time, andtiming meansfor generating a plurality of clock signals having a time duration muchshorter than the time between said two sequential positions, and whereinsaid program means is adapted to compute a plurality of Z point signalsindicative of the desired vertical position of said bonding tool at eachclock signal division between said two sequential positions, positionindicating means coupled to said Z drive motor for generating an outputsignal indicative of the actual position of said bonding tool, and saidprocessor control means being adapted to receive said Z point signalsand said output signals and to generate a forcing function forpositioning said Z drive motor and said bonding tool to a desiredvertical position.
 45. A processor controlled Z drive apparatus as setforth in claim 44 wherein said program means is adapted to compute andstore said Z point signals indicative of all of the desired verticalposition of said bonding tool between two sequential positions, and tocompare the output signal of said position indicating means with a Zpoint signal approximately one time signal removed from the computeddesired signal in the direction of movement of said bonding tool.
 46. Aprocessor controlled Z drive apparatus as set forth in claim 45 whereinthe last forcing function generated by said processor control means is asignal calculated to move said bonding tool from its actual indicatedposition to the second of said two sequential positions.